During surgery, anesthesiologists administer one or more drugs, which can include but are not limited to Propofol and the like, to sedate or relax patients while undergoing surgical procedures. It is the anesthesiologist's responsibility to ensure that the correct level of drug is provided to the patient to ensure, among other things, that the patient is not too heavily sedated (which could lead to issues such as longer recovery times, or, in extreme cases, even death), or not sedated enough, which could lead to the patient waking up or not being fully unconscious and hence being aware of the surgical procedure, perhaps even feeling pain. Other things that would be of benefit to the anesthesiologist can include the ability to check for perfusion of the drug(s) across cerebral hemispheres to ensure that both sides of the brain are affected by the drug, as well as the ability to keep a patient “just unconscious” so they could quickly be awoken for checking responses etc. (the latter being common during neurology procedures as an example).
Under current practices, anesthesiologists generally use tools such as the Bispectral index (e.g. via a BIS monitor) in an attempt to measure depth of anesthesia. A BIS monitor tool uses electrode(s) attached to the patient's forehead and purportedly gives a useful measure of depth of anesthesia. However, a BIS monitor suffers from a number of drawbacks. One concern is that it does not rely on any underlying physiological model of brain function or generation of awareness. Another problem is that the BIS number is insensitive to several commonly used anesthetic agents and therefore it is questionable to what degree it indicates awareness. Additionally, the calculations performed by a BIS monitor are computer-intensive. In view of the questionable reliability and practicality of a BIS monitor, the medical community generally uses such tools as a guide rather than a definitive answer to anesthesia level. Anesthesiologists also use other measures in conjunction with BIS readings in an effort to gauge the patient's state. Such measures can include pupil size, heart rate, respiration, sounds from the patient, and others. However, the effectiveness of these measures relies on subjective assessment by the anesthesiologist and are therefore potentially subject to human error.